Abrasives are used in three basic forms: loose particles, particles bonded with various agents into rigid forms, and particles deposited on flexible bases. This invention pertains to abrasive particles bonded into fixed, rigid forms.
All effective abrasives wear as they grind. The lifetime of an abrasive tool is determined by the wear or failure of the abrasive particles and by the adherence of the particles to the rigid base or core of the tool.
Rigid abrasive tools often are manufactured by applying abrasive particles mixed with a bonding agent, to form a composite material, to the cutting or grinding surface of the tool. The composite material is placed onto surfaces of various shapes, such as wheel, segmental, or stick shapes. In older abrasive tools, the bonding agent was often resinoid or ceramic, but in recent years the use of metallic bonding agents, such as electroplated nickel, cobalt, bronze or a bronze alloy, has become increasingly common. The particles are commonly cubic boron nitride, diamond or silicon carbide.
In addition to lifetime considerations, the effectiveness of grinding tools is also affected by loading-up of the grinding surface with material removed from the work piece. Therefore, a grinding surface having low coefficient of friction between the abrasive particles offers additional benefits by decreasing the amount of loading-up.
The use of a thin coating for prolonging the life of cutting surfaces of metal-working tools has been suggested. U.S. Pat. No. 5,308,367 discloses the use of a titanium nitride or titanium carbide coating over the abrasive particles of grinding tools. A physical vapor deposition process is proposed to produce cubic boron nitride tools coated with titanium nitride or other metal compound coatings of uniform composition.
There is continued need for abrading or grinding tools having metal-bonded grains or particles in which a coating is applied to increase the lifetime of the tools.